feat(cu): send non-persisted process message as first message on cold start

[TillaTheHun0]

This PR makes it so the CU will send an initial message to the module, on process cold-start, that represents the process, itself.

This will need to include the Data, Signature, and Anchor of the process, so the CU needed to start persisting those values with the cached process in its db as well.

This initial "process" message evaluation is not persisted by the CU. Only "real" message evaluations are persisted.

Also cleaned up, using nullish() instead of .optional() or even more verbose .optional().nullable() when in all cases we're just interested in null | undefined which is precisely the use case of nullish()

Closes #293